During normal use contact lenses become soiled or contaminated with a wide variety of compounds that can degrade lens performance. For example, a contact lens will become soiled with biological materials such as proteins or lipids that are present in the tear fluid and which adhere to the lens surface. Also, by handling of the contact lens, sebum (skin oil) or cosmetics or other materials can soil the contact lens. These biological and external contaminants can affect visual acuity and patient comfort. Accordingly, it is important to remove such contaminants from the lens surface for continued comfortable use with a lens care solution that contains one or more cleaning components.
Ophthalmic compositions formulated as a lens care solution must also contain one or more antimicrobial components. Presently, the two most popular antimicrobial components are poly(hexamethylene biguanide), often referred to as PHMB or PAPB, and polyquaternium-1.
Lens care solutions with PHMB represent a significant improvement in patient comfort and antimicrobial effectiveness compared to most other antimicrobial components. However, as with any antimicrobial component there remains a trade-off between the concentration of the antimicrobial component in the solution and the comfort experienced by the patient. Due to its wide commercial acceptance, extensive efforts have been directed to improve the antimicrobial efficacy or the patient comfort profile by chemically modifying PHMB.
An alternative approach to improving patient comfort has been the introduction of comfort agents or hydrating agents to the lens care solutions. For example, U.S. Pat. No. 7,135,442 describes the use of dexpanthenol in combination with the sugar alcohol, sorbitol. It is said that the dexpanthenol helps to stabilize or minimize the disruption of the aqueous lachrymal layer by surfactants present in the lens care solutions.
Hyaluronic acid is a linear polysaccharide (long-chain biological polymer) formed by repeating disaccharide units consisting of D-glucuronic acid and N-acetyl-D-glucosamine linked by β(1-3) and β(1-4) glycosidic linkages. Hyaluronic acid is distinguished from the other glycosaminoglycans, as it is free from covalent links to protein and sulphonic groups. Hyaluronic acid is ubiquitous in animals with the highest concentration found in soft connective tissue. It plays an important role for both mechanical and transport purposes in the body, e.g., it gives elasticity to the joints and rigidity to the vertebrate disks, and it is also an important component of the vitreous body of the eye.
Hyaluronic acid, because of its high degree of hydration, is likely responsible for increasing the resistance of biological tissues or cells to compression. Also, the viscoelastic properties of hyaluronic acid, that is, hard elastic under static conditions though less viscous under small shear forces enables hyaluronic acid to basically function as a shock absorber for cells and tissues. The hyaluronic acid properties are dependent on the molecular weight, the solution concentration, and physiological pH. At low concentrations the individual chains entangle and form a continuous network in solution, which gives the system interesting properties such as pronounced viscoelasticity and pseudoplasticity that is unique for a water-soluble polymer at low concentration.
U.S. Pat. No. 5,770,628 by Cantoro describes an artificial tear composition that contains from 0.05 to 2 wt. % of hyaluronic acid. Cantoro also recognized that if one were to add a poloxamer surfactant to the artificial tear composition one could use the composition as a rewet drop. The poloxamer surfactant is said to remove denatured tear proteins and other contaminants from extended wear contact lenses while the lenses are being worn. See, U.S. Pat. No. 6,528,465.
PCT Application (Publication No. WO 01/057172) describes a multi-purpose solution to remove protein deposits from the lenses as well as to disinfect or preserve the lenses. The described solutions include a polysaccharide with a molecular weight of 5000 daltons or greater as a non-enzymatic protein remover (0.005 to 10 wt. %), a non-ionic surfactant (0.01 to 10 wt. %) and a polymeric preservative (0.00001 to 1 wt. %). An exemplary solution is provided as Example No. 5. This solution includes 0.02 wt. % sodium hyaluronate, 1.0 wt. % poloxamine (Tetronics® 1107), 0.125 wt. % Na2EDTA and 1 ppm of PHMB in a phosphate buffer.
There remains an interest and need for improved ophthalmic compositions, particularly, a multi-purpose lens care solution, that offers an improved patient comfort profile without having to sacrifice antimicrobial efficacy.